1. Field of the Invention
The present invention relates to improvement in or relating to a semiconductor photoelectric conversion device which has a light-transparent substrate, a light-transparent conductive layer formed on the substrate serving as a first electrode, a non-single-crystal semiconductor laminate member comprised of a P- or N-type first non-single-crystal semiconductor layer formed on the first electrode, an I-type second non-single-crystal semiconductor layer formed on the first non-single-crystal semiconductor layer and a third non-single-crystal semiconductor layer formed on the second non-single-crystal semiconductor layer and opposite in conductivity from the first non-single-crystal semiconductor layer, and another conductive layer formed on the non-single-crystal semiconductor laminate member serving as a second electrode.
Also, the invention pertains to a method for the manufacture of such a semiconductor photoelectric conversion device.
2. Description of the Prior Art
In conventional semiconductor photoelectric conversion devices of the abovesaid type, the conductive layer serving as a first electrode and the non-single-crystal semiconductor laminate member usually form therebetween a flat and smooth boundary.
In such a case, since the area of contact between the conductive layer serving as a first electrode and the non-single-crystal semiconductor laminate member is not greater than the area in which they are opposed, there is a limit to the reduction of the contact resistance between the conductive layer serving as a first electrode and the non-single-crystal semiconductor laminate member, imposing certain limitations on enhancement of the photoelectric conversion efficiency.
Furthermore, the non-single-crystal semiconductor laminate member and the conductive layer serving as a second electrode also form a flat and smooth boundary therebetween.
With the conventional semiconductor photoelectric conversion device of such a structure, light which is incident on the light-transparent substrate on the side opposite the conductive layer serving as a first electrode and passes thereinto via the substrate, mostly enters into the non-single-crystal semiconductor laminate member, but a portion of the light is reflected at the boundary between the conductive layer serving as a first electrode and the non-signle-crystal semiconductor laminate member and back to the outside through the conductive layer and the light-transparent substrate.
The light having entered into the non-single-crystal semiconductor laminate member travels therein in its thickwise direction, creating electron-hole pairs. When the light propagates in the non-single-crystal semiconductor laminate member from the boundary between it and the light-transparent conductive layer serving as a first electrode to the boundary between it and the conductive layer serving as a second electrode, the light travels only a distance equal to the thickness of the non-single-crystal semiconductor laminate member.
Holes (or electrons) of the electron-hole pairs generated in the non-signle-crystal semiconductor laminate member flow across thereto to reach the light-transparent conductive layer serving as a first electrode, and the electrons (or holes) flow across the non-single-crystal semiconductor laminate member to reach the conductive layer serving as a second electrode, developing electromotive force across both conductive layers.
In this case, the maximum value of the difference between the thickness of the non-single-crystal semiconductor laminate member and the thickness of its first non-single-crystal semiconductor layer formed in contact with the conductive layer serving as a first, electrode cannot be selected greater than the maximum diffusion length over which the electrons (or holes) of the electron-hole pairs, created at and in the vicinity of the boundary between the first non-single-crystal semiconductor layer of the non-single-crystal semiconductor laminate member formed in contact with the conductive layer serving as a first electrode and the second non-single-crystal semiconductor layer formed thereon, can flow to reach the conductive layer serving as a second electrode.
Therefore, when light travels in the non-single-crystal semiconductor laminate member from the boundary between it and the conductive layer serving as a first electrode to the boundary between it and the conductive layer serving as a second electrode, the light does not travel in excess of the abovesaid maximum diffusion length in the region from the boundary between the first non-signle-crystal semiconductor layer of the non-signle-crystal semiconductor laminate member formed in contact with the conductive layer serving as a first electrode and the second non-single-crystal semiconductor layer formed thereon to the boundary between the non-single-crystal semiconductor laminate member and the conductive layer serving as a second electrode.
For the reason given above, the prior art semiconductor photoelectric conversion devices are extremely poor in efficiency of utilization of incident light, and hence it has been very difficult to achieve a photoelectric conversion efficiency higher than 8%.